Neurons are electrically excitable cells that process and transmit information around the nervous system. Neurons are the primary components of the brain and spinal cord in vertebrates, and ventral nerve cord in invertebrates.
Referring to FIG. 1, a neuron includes a nucleus as shown. The nucleus includes a soma, an axon, and a dendrite. The soma acts as a processing unit for processing of neuronal signals and is responsible for generating action potentials (i.e., voltages). Action potentials (also referred to as electrical signals herein) are further described below. The action potentials are propagated from the soma, through an axon, to the end of the neuron, which is also called an axon terminal. In the axon terminal, chemical neurotransmitters that chemically encode the electrical signal are produced, which cross a gap between the axon terminal and a dendrite of another neuron (not shown). This gap is part of the connection system of two neurons. The gap is referred to as a synapse. The synapse is descried more fully below in conjunction with FIG. 2.
Attempts have been made to emulate operation of a synapse with electronic circuits.
So-called spike timing dependent plasticity (STDP) is known to exist in synapses. However, existing circuits are unable to emulate spike timing dependent plasticity in a way that closely replicates biochemical processes.
It is also known that there are variety of types of spike timing dependent plasticity that are experimentally observed, each dependent upon a relative timing between presynaptic and postsynaptic stimuli and also dependent upon waveform shapes of postsynaptic back potentials. Existing circuits are unable to emulate all of the different types of STDP.
A so-called BCM rule, described more fully below, is also known. Existing circuits and techniques are unable to provide a relationship between the BCM rule and STDP.
Therefore, it would be desirable to provide a circuit and a method that can emulate spike timing dependent plasticity in a way that closely replicates biochemical processes. It would also be desirable to provide a circuit and a method that can emulate all of the different types of STDP. It would also be desirable to provide a circuit and a method that can provide a relationship between the BCM rule and STDP.